scripts/unit-test.py: Rework handling of directories in clone_pkg()
scripts/unit-test.py: Rework handling of directories in clone_pkg()

This makes things a bit neater and accounts for directories that might
already exist as a result of the docker build process.

Tested: Ran run-unit-test-docker.sh, confirmed expected functionality

Change-Id: Ieebd63da0383e4431ae9cdf972e8905aff96f175
Signed-off-by: Andrew Jeffery <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@aj.id.au>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts